Ultra high frequency electric discharge devices



June 19, 1951 w. J. sc 'rT ET AL 2,557,771

Filed July 11, 1947 2 Sheets-Sheet 1 ULTRA HIGH FREQUENCY ELECTRIC DISCHARGE DEVICES Fig.1. 1a Fig.2.

i /8 l :35 -11 g \I/ I I I l I r I i I i i 25 2a 30 as 1 Ihventors: a WHham J Scott,

,0 Robert Latham, 9 y Their Attovney.

June 19, J SCOTT r 2,557,771

ULTRA HIGH FREQUENCY ELECTRIC DISCHARGE DEVICES Filed July 11, 1947 2 Sheets-Sheet 2 IIIIII'III,

IhVntbts: WHIiaYn J. Scott, Robert Latham, by 79 44 6. J

- Them Attovn ey.

Patented June 19, 1951 ULTRA HIGH FREQUENCY ELECTRIC DISCHARGE DEVICES William J. Scott and Robert Latham, Rugby, England, assignors to General Electric Company, a corporation of New York Application July 11, 1947, Serial No. 760,302 In Great Britain July 9, 1941 Section 1, Public Law 690, August 8, 1946 Patent expires July 9, 1961 3 Claims. 1

This invention relates to velocity modulated electron discharge oscillators and systems of the reflex oscillation type in which ultra high frequency electric oscillations are set up in a hollow cavity or confined field resonator.

In such devices an electron beam of uniform velocity is passed axially through an oscillating electric field produced at the annular gap of an electrical cavity resonator. Cyclic variations in velocity are imparted to the electrons, resulting in bunching or grouping of the electrons at a point further along the beam. An electron mirror or reflector electrode placed in the path of the beam sends electrons backwardly by true reflection or as secondary electrons emitted by reason of impingement of the primary electrons of the beam. All or only suitable groups of the electron beam return through the gap in bunches of correct phase and thereby impart energy to the resonator. Power may be abstracted from the resonator by a conducting wire loop linked with its internal magnetic field.

It has been proposed to tune such oscillators by varying the gap spacing of the resonator so that one tube may produce oscillations variable over a relatively wide range of frequency. It is found, however, that in order to maintain satisfactory oscillation conditions, it is necessary when changing the gap width to make a corresponding change in the beam velocity.

It is the object of the present invention to provide a new and improved ultra high frequency discharge device or oscillator of the velocity modulation type.

It is a further object of the invention to provide a new and improved reflector type velocity modulation discharge device.

It is a still further object of the invention to provide means whereby the oscillation frequency of a reflex oscillator may be changed without the necessity of more than a single main adjustment.

The invention is based on the discovery that, provided the change in the gap width in a reflex oscillator of the type described is accompanied with acorrelated change in the spacing between the reflector or secondary emission electrode and the edge of the gap nearest the reflector, optimum oscillation conditions are maintained without any change inlthe beam velocity, although the oscillation frequency is altered.

According to the present invention, the part of the cavity resonator which is nearer to the reflector electrode is rendered movable with relation to the remainder thereof and to the reflector electrode so that, when the annular gap is changed to vary the oscillation frequency, a correlated change takes place in the spacing between the adjacent edge of the gap and the reflector electrode, such as to render unnecessary a change in the beam velocity.

In carrying out the invention, use may be made of a resonatin chamber having a flexible wall, bending of which permits an alteration in the width of the annular gap and a consequent alteration in the resonant frequency of the resonator. The resonating chamber may be in the form of a hollow annulus of generally rectangular cross-section, in which the walls around a central aperture are depressed into the form of conical frusta having their apices oppositely directed, the inner and smaller rims of the frusta being adjacent and forming the annular gap through which the electron beam is projected. The discharge tube is then completed by means of two glass stems which are secured in a gas tight manner to the walls of the resonator, one of the stems supporting an electron gun and the other conveying the lead-in conductor to the refleeting electrode, the gun and the reflecting electrode being disposed axially of the resonator and on opposite sides of the central aperture therethrough.

In order to vary the width of the annularv gap, the parallel walls of the resonator are moved toward or away from one another, reliance being placed on the flexibility of one of the walls to enable this movement to be effected. In order, however, to insure that as the gap width varies a corresponding variation takes place in the spacing between the reflector electrode and the edge of the gap nearer thereto, it is necessary to maintain constant the distance between the reflector electrode and the far edge of the gap. For this purpose the glass stems carrying the reflector electrode may be rigidly supported with respect to that wall of the resonating chamber to which the stem carrying the electron gun is attached, while means is provided for movin the other wall of the resonating chamber relatively to the fixed wall and the reflector electrode.

An alteration of the gap width, being correlated with a change in the distance between the inner edge of the gap and the reflector or secondary emission electrode is found to be accompanied by defocusing of the electrons returning from the reflector electrode. This defocusing is believed to be due to the alteration of the shape of the electron lens formed by the reflector electrode and the near edge of the gap. In order to overcome the defocusing eflect, according to a further feature of the invention, additional electrode means is located between the reflector electrode and the resonator, the further electrode bein maintained at the voltage of the resonator and being fixed in position relative to the reflector electrode. The further electrode may be joined electrically to the resonator by being directly supported from the transverse rigid wall which is in fixed relation with the reflector electrode. electrode may be formed as a metal plate or washer pierced with an aperture arranged symmetrically with respect to the axis of the beam.

For a better understanding of the invention, reference may be made to the following description taken in connection with the accompanying drawings and its scope will be pointed out in the appended claims. Fig. 1 is a section of a velocity modulated electron discharge oscillator constructed in accordance with the invention; Fig. 2 is a modified form of the construction shown in Fig. l with the end stems omitted; Figs. 3 and 4 are views similar to Fig. 2 of an arrangement embodying the additional electrode for preventing defocusing of the beam; and Figs. 5 and 6 are further modifications ShOWing. different means for effecting the variation of the gap width.

Referring now to Fig. 1, there is indicated a velocity modulated electron discharge oscillator comprising an electron gun I arranged to produce a beam of electrons which is projected across the annular gap 2 of a hollow annular cavity resonator 3. of conductive material of generally rectangular shape in cross-section, the beam after passage through the gap 2 of the anode or resonator 3. being influenced by reflector electrode 4. The electrode 4. may be used either solely as a. reflector or as. a secondary emission electrode. The resonator 3 is constructed with one of its parallel walls 5 sufiiciently rigid to resist deformation, while its other parallel Wall 6 is made in the form of a flexible diaphragm. The electron gun I. is ri idly supported with relation to the Wall 5 by means of a metal tube 1- secured, as by welding at its upper end, to the wall 5 and at its lower end supporting a glass stem 8 which carries the gun I and its appropriate lead-in conductors 9, l9 which energize a filamentary heater l-l used for heating the emissive surface or cathode of the electron gun i and for supplying potential to the electrode II which concentrates the emitted electrons into a beam accelerated by the positive potential of anode 3. The lead-in conductor I2 to electrode 4 is led through a similar glass stem l-3 sealed to a metal tube l4: secured to the wall 6 of the cavity resonator 3. A flexible connection 15 is interposed between the lead 9 and the electrode 4 for a purpose to be referred to hereinafter. Secured to the tube [4. is a transverse rigid plate or ring it by movement of which relatively to the wall 5 the diaphragm 6 can be flexed with a resultant change in the width of the gap 2.

If, when adjustment of the resonant frequency of the resonator 3 is made by effecting a change in the width of gap 2, the axial spacing between electrode 4 and the near or adjacent edge of the gap 2 is maintained constant, it has been found necessary to make a correlated change in the beam voltage, i. e., the voltage impressed between the anode structure 3 and the electron gun l, to maintain oscillation. The frequency and voltage change substantially linearly with change in the width of gap 2 and, moreover, there may be. two ormore voltages at which the electron The further discharge device will oscillate at any one frequency. In practice, this voltage change is undesirable as it involves the adjustment of two controls when adjusting the frequency. Furthermore, the power output of the tube changes considerably with change in impressed voltage so that a further advantage is obtained if the beam voltage can be maintained constant with the change in frequency.

We have found that, if the distance between the electrode 4 and the far or lower edge of the gap 2 remains constant while the gap width is changed, an alternation in frequency may be made without a correlated change in beam voltage. To this end, the electrode 4 is supported, in the arrangement shown in Fig. 1, upOn a U- shaped insulator I! the limbs of which are secured, e. g. by metal straps l8, to the metal tube 1, the support wire for the electrode 4 being sealed through the bight of the U-shaped insulator. Apertures i9, 20 are made in the walls 5 and 6 of the resonator through which the limbs of insulator ll may pass. The flexible lead l5 permits a relative movement between the stem I3 and the electrode 4 when the gap width is altered.

It has been found that, with the arrangement according to the invention, a tube having a, resonator 1 in diameter and long axially covers a range from 3200 to 4000 megacycles per second for a gap change of 2 mm. without requiring a change in beam velocity.

The arrangement illustrated in Fig. 2 provides a construction more suited to production methods than that illustrated in Fig. 1. In this construction the electrode 4 and its carrying stem l3 are rigidly supported with respect to the rigid transverse wall 5 of the resonator by being mounted on a transverse rigid wall portion 21 of the envelope of the tube which is connected to the wall 5 by means of a plurality of screwthreaded pillars 22, of which only one is illustrated. The flexible diaphragm G is connected to a tubular member 23 which is, in turn, connected with a second diaphragm 24 flanged at its outer end and secured to the wall portion 2|. Attached to the tubular part 23 is a transverse member 25, which also engages the pillars 22 and which by means of adjusting nuts may be moved axially in order to move the flexible wall 5 of the resonator and change the width of the gap 2. In order to derive ultra high frequency energy from the resonant cavity 3, there is provided output electrode means in the form of a loop 26 coupled to the resonator 3 and connected to an output lead 27 sealed in air tight relation with respect to the resonator 3 by means of an insulating seal 28.

As mentioned previously, it has been found that a change in the width of gap 2, being associated with a change in the spacing between the near edge of the gap and the electrode 4, results in a slight defocusing of the electrons which after transversing the gap 2 are reflected by electrode 4 and re-enter the resonator or anode 3 to deliver energy to the electromagnetic field thereof. This is avoided in accordance with the arrangement illustrated in Fig. 3 by means of a further electrode 29 arranged between the electrode 4 and the cavity resonator 3 and tied, in voltage to the resonator and in position to the reflector 4. The electrode 29 may consist of a disk having a central aperture 30 aligned with the aperture through the resonating chamber and is supported by meansof one or more wires or metal tabs 3| which are secured to the plate 2|. By this means, the position of the electrode 29 is fixed with relation to the electrode t and its voltage is maintained at that of the resonator or anode 3.

Fig. 4 shows a modified construction of the arrangement shown in Fig. 3 wherein the upper wall 6 of the resonator is made rigid, while the lower wall 5 is constituted by a flexible diaphragm. The further electrode 29 is, in this modification, secured to the wall 6 so as to constitute a portion of the wall of the envelope of the discharge device and it is secured near its inner end to the tube M so as to maintain constant its spacing from the electrode 4. By making electrode 29 in the form of a flexible diaphragm movement of the upper wall 6 of the resonator 3 is made possible with relation both to the electrodes 4 and 29.

In the arrangement shown in Figs. 5 and 6, the flexible wall of the resonating chamber 3 is rigidly supported at its inner and outer ends upon the tubular member id and the rigid wall 5 of the resonator, respectively. In Fig. 5, the part constituting the upper wall of the resonator at the gap 2 is formed by a rigid frusto-conical member 32 securedat its outer and upper end to the flexible wall 5. Displacement of the member 32 to effect a change in the gap width is secured by attaching it, by means of screw-threaded pillars 33, to a transverse rigid member 3 having a central aperture 35 for the passage of the stem it, the member 3 3 being made adjustable with respect to the transverse wall 36 attached to the tubular member Id by any suitable means, such as the threaded pillars 31 and the nuts associated therewith.

In Fig. 6 a somewhat modified construction of the frusto-conical part which defines the gap of the cavity resonator is adopted by means of which the effective resonating portion 38 of the cavity resonator 3 is considerably reduced in size with consequent increase in its resonant frequency. In this form of the invention, the gap 2 is defined by the two frusto-conicalmembers 39, so having their apices oppositely directed, the former of which members is made integral with the rigid transverse wall 5 and the latter of which is attached, by means of an axial wall ti and a H transverse wall G2, to the flexible wall 6 of the cavity resonator 3. Energy may be abstracted from the effective resonating chamber 38 by any suitable output electrode means, such as the coupling loop 43, having one of its ends connected to the inner surface of the walls defining the chamber 38 and its other end connected to the inner conductor is of a concentric transmission line, the outer conductor of which is connected to the wall of chamber 38. In other respects the construction of Fig. 6 is similar to that shown in Fig. 5.

While we have shown and described the invention as applied to an electric discharge device employing electrodes of particular configuration, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention and we, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States, is:

1. An electric discharge device of the reflex velocity modulation type including a resonator having spaced generally parallel walls, said walls being apertured to provide a gap between said walls, across which electrons may travel, an envelope section sealed to the exterior of one of said walls at a region encircling the aperture therein, a cathode supported within said envelope section, said one wall being rigid, a refleeting electrode positioned in alignment with the opening in the other wall and on the side of said resonator opposite said cathode, said other wall being sufiiciently flexible to permit adjustment of the spacing between said walls at said means rigidly supporting said reflecting elec trode from said one wali of said resonator and a second envelope section enclosing said reflecting electrode sealed to said other wall of said resonator.

2. An electric discharge device of the reflex velocity modulation type including a resonator having spaced generally parallel walls, said walls being apertured to provide a gap between said walls across which electrons may travel, an envelope section sealed to the exterior of one of said walls at a region encircling the aperture therein, a cathode supported within said envelope section, said one wall being rigid, a reflecting electrode positioned in alignment with the opening in the other wall and on the side of said resonator opposite said cathode, said other wall being sufliciently flexible to permit adjustment of the spacing between said walls at said gap, insulating means extending through said resonator on opposite sides of said openings and rigidly supporting said reflecting electrode from said one wall of said resonator and a second envelope section enclosing said reflecting electrode and sealed to said other wall of said resonator.

3. An electric discharge device of the reflex velocity modulation type comprising a resonator having opposed wall portions provided with aligned apertures through which electrons may pass, one of said walls being rigid and the other of said walls being flexible in the region surrounding the aperture therein, an envelope section sealed to the exterior or" said one wall at a region encircling the aperture therein, a cathode supported in said envelope section, a second envelope section sealed to said other wall about the aperture therein and including two rigid wall sections and an interposed flexible wall section, a reflecting electrode supported from the rigid wall section remote from said resonator, rigid means extending laterally respectively from the rigid wall of said resonator and from each of the rigid wall sections or" said second envelope section, means extending in the direction of the gap between the walls of said resonator coupling said rigid means together and providing for the movement of the intermediate rigid means relative to the two outer rigid means to adjust the gap width without altering the distance between the rigid wall of the resonator and said reflecting electrode.

WILLIAM J. SCOTT. ROBERT LATHAM.

Name Date Harrison et a1 Jan. 21, 1947 Number 

